1. Field of the Invention
This invention relates generally to the evaluation of the physical properties of samples, and more specifically, to methods employing near-infrared spectrophotometry to simultaneously quantify various physical properties of a multicomponent sample, particularly hydrocarbons.
2. Description of the Prior Art
The need often arises to quantify the physical properties of different gaseous or liquid samples used at various stages of industrial chemical processes. For example, it is frequently required to measure the heats of formation and molecular weights of hydrocarbons being used in petroleum processing and refining.
In the past, the physical properties of samples have typically been measured one property at a time, using testing methods which have been developed to specifically evaluate one particular property. For example, the heat of formation of a particular sample has been determined by actually burning the sample in a calorimeter. Similarly, molecular weight of a sample has been determined by inducing and measuring viscous flow of the sample using a viscometer. In each of these examples, however, the physical test methods measure, or quantify, the physical properties by actually subjecting the sample to the conditions in question. To measure more than one physical property of a particular sample, a plurality of tests must be individually conducted on a plurality of samples. Such an approach to measuring the physical properties of a sample is slow, expensive, and univariate.
More recently, near-infrared spectrophotometric analysis has been used to determine indirectly the qualitative properties of various samples. Such methods are disclosed in Wetzel, D. L. Anal. Chem 1983, 55, 1165A to 1176A; Watson, C. A. Anal. Chem 1977, 49, 835A-840A, incorporated herein by reference. For example, near-infrared spectrophotometric analysis has been employed to determine the baking quality of flour as shown in Star, S.; Smith, D. B.; Blackman, J. A.; Gill, A. A. Anal. Proc. (London) 1983, 20, 72-74; to determine digestibility of forages as shown in Winch, J. E.; Helen, M. Can. J. Plant Sci. 1981,, 61, 45; Norris, K. H. Barns, R. F.; Moore, J. E.; Shenk, J. S. Animal Sci. 1976, 43, 889-897; and to determine the potencies of pharmaceutical drugs as shown in Rose, J. J. The Pittsburgh Conference, Atlantic City, NJ, March, 1983; paper 707. Each of the above references is incorporated herein by reference.
Use of near-infrared spectrophotometric analysis has many advantages over other methods since it is rapid, relatively inexpensive, and multivariate in that many properties can be tested for simultaneously. To date, however, methods have not been available to use near-infrared spectrophotometric analysis to directly quantify the physical properties of samples, such as the molecular heat and weight of hydrocarbons.
The need existed to develop methods for using near-infrared spectrophotometric analysis to effeciently and inexpensively quantify various physical properties of samples.